1. Field of the Invention
The present application relates generally to an improved method for producing hydrocarbons from a reservoir. More particularly, the subject invention concerns the creation of an inverted drainhole having an inverted or upwardly inclining bore into a producing interval starting from a generally vertical wellbore which extends from the surface and a method for drilling, completing, and producing utilizing such an inverted drainhole.
2. Prior Art
A conventional method to produce hydrocarbons has been to drill a wellbore in an essentially vertical direction from the surface through a subterranean reservoir using standard bits, motors and drill pipe. In reservoirs that are relatively thin, this method exposed only a small portion of the pay zone, or producing formation, to the wellbore, and thus limits productivity. Also premature gas coning and/or water coning in such wells often reduced the amount of oil or gas that could be recovered. Coning is a formation phenomena in which the contact (or interface) between a layer of oil and either water or gas assumes a peculiarly cone shape and thereby allows early production of the offending fluids and reduces the amount of valuable oil or gas available to be produced.
Within the past decade, it has become increasingly common to drill at least a portion of the wellbore so that it intersects the reservoir from the top and at a high angle off vertical. In some cases this is a high angle of from 83 to about 88 degrees off vertical, or even horizontal (90 degrees off vertical). High angle or horizontal sections can then be extended laterally from the top through the pay zone by 1000 to 3000 feet or more, or through a plurality of pay zones which may be separated by fault blocks, shale stringers, or other barriers to horizontal or vertical permeability. Development of high angle drilling techniques has meant that more of the pay zone can be exposed to the wellbore, and that oil or gas can be produced at a faster rate while potentially recovering more of the original oil in place than would be otherwise possible with a conventional vertical or even directional well (less than 83 degrees off vertical). This is generally called “directional drilling” or “horizontal drilling”. The standard equipment utilized to drill these conventional laterals includes—a whipstock, bits, motors, bent subs, monel pipe, gyroscopes and other directional tools.
Prior attempts to install lateral boreholes in a well include Collins, Jr (U.S. Pat. No. 4,421,183) which discloses an apparatus for penetrating the sidewalls of boreholes. Other efforts include U.S. Pat. Nos. 2,404,341, 4,396,075, 4,402,551 and 4,415,205.
Current directional drilling methods and equipment can install lateral or directional laterals or drainholes that are important to relieve pressure in the formation and increase production of the oil or gas product. These direction laterals or drainholes exit the mostly vertical wellbore at a generally downward vertical angle and then out to increasing angles as the depth is increased. Thus the entrance vertical point is higher in elevation than the formation target. Even the end point of the lateral or drainhole is generally the lowest point of the full lateral or drainhole. The curvature to get these laterals from vertical to horizontal can be 90 feet radii to several hundred feet radii. This radius is kept so high to allow the drill equipment to function, to allow production pumps to be run through the curve section and installed in the bottom level or to run certain tools to the end of the lateral. Pumps must be run through the curve section to pump the well's fluid from the lowest point possible to maximize productivity. However, significant problems occur in running pumps through this long curved section—including rod wear, stuck tools, smaller pumps. Also such a long radius means that the curve must be started higher up the hole starting in rocks or formations that are difficult and/or expensive to drill. Also, such long curves mean that it takes longer to drill and adding length to the drilled section.
Of course, may variations can occur, including increasing the upward angle toward the end of the lateral. Another problem with current directional drilling practices is that solids from the formation and from the drilling, production and/or completion process or other from sources can build up in the lowest part of the lateral section and cannot be lifted up and out of the well by production fluids to clear the installed lateral. This can reduce, stop or interfere with production.
Another problem with current directional or horizontal drilling practices is that liquids also can build up in the lateral in the lowest points and cannot be cleaned out in normal flow processes. Such liquid buildup can cause an increased liquid saturation in the surrounding formation rock at the lowest point of the laterals and prevent gaseous flow due to backpressure, relative permeability reduction or capillary pressure restrictions.
Other problems with current directional or horizontal drilling practices is the requirement of putting force or “weight on bit” on the bit so that the rock can be crushed, cut and ground up. Also the rotational requirement for the bit requires significant additional effort and increased wear in shorter radii turns.
An inverted lateral or drainhole, that is one that is not drilled in a generally downward direction, but is drilled in a generally upward direction from the primary mostly vertical wellbore such that it is slanted upward and outwards into the formation and would encourage liquids to drain out of the lateral or drainhole, and solids to flow out with liquid flow and/or for gas saturation to remain in the lateral drainhole to maximize gas flow. Previous art in this area includes U.S. Pat. No. 4,431,069 Dickinson and U.S. Pat. Nos. 4,605,076/4,646,835 Goodhart. That existing art utilized standard drilling tools including bits and motors and required rotation of the full or part of the drill pipe. Such an reverse drainhole arrangement would allow a pump to be placed in the generally vertical primary well bore below the intersections or exit points of the inverted laterals. This would allow a larger pump that could be easily repaired and that can service several or many inverted laterals or drainholes.
The creation of such inverted laterals or drainholes has not been described or utilized in the prior art and is needed to address the limitations of existing drainhole or horizontal lateral technology.